1. Field of the Invention
The present invention relates to regenerative apparatus and regenerative methods for thermally treating gases, and in particular, to systems for circulating blocks in order to transfer heat.
2. Description of Related Art
Increasingly stringent environmental laws have required manufacturers and various businesses to reduce the amount of polluting or toxic emissions from various processes, especially emissions of volatile organic compounds ("V.O.C."). For example, waste solvent vapors, and various hydrocarbon fumes can be produced from printing processes, or from baking, or cooking. Some industrial processes produce such toxic emissions as benzene, formaldehyde, etc.
Such pollutants can be eliminated by heating them to the point where they decompose into non-toxic components such as water vapor or carbon dioxide. A disadvantage with such thermal decomposition is the relatively high cost of heating the pollutants. Thus a significant effort has been made to reduce the energy required for this thermal decomposition.
One known method for conserving energy is to use a heat exchanger to return the heat from the exhaust of a furnace to preheat air entering the furnace. Such preheaters have used heat exchangers of various types.
In U.S. Pat. No. 3,404,965 a drum is peripherally fitted with a number of porous ceramic blocks. The drum rotates around a horizontal axis between a gas inlet and outlet on opposite sides of the drum. A burner heats the inside of the drum to thermally decompose pollutants delivered to the inside of the drum. The thermally cleansed gas exits through the porous ceramic blocks and heats them. The heated blocks circulate to an upstream position so that the incoming gas stream is preheated by passing through the heated ceramic blocks.
One disadvantage with U.S. Pat. No. 3,404,965 is that the porous ceramic blocks present to the incoming gas stream a converging cross section. Thus incoming gas would accelerate if kept within the blocks. This undesirably reduces the residence time in the porous blocks. Moreover, the sides of the block are open so that incoming gas will either be driven to accelerate or take the path of least resistance and leak through the sides of the converging block.
Also, the structure of U.S. Pat. No. 3,404,965 is arranged to inject and withdraw gas only over about half the circumference of the drum. This inability to use a greater number of the porous blocks decreases efficiency.
Also, this drum is completely enclosed in the hot interior of a casing lacking effective seals. For this reason, the casing enclosing the drum and the moving parts is double walled and insulated. Consequently, the moving parts inside the casing tend to be overheated. Also, incoming gas can escape to the casing surrounding the drum to eventually bypass the porous ceramic blocks.
In U.S. Pat. No. 3,718,440 a ceramic disc having a number of triangular passages rotates past the inlet and outlet of a combustion chamber to return exhaust heat to the incoming gas stream. Various moving parts and bearings associated with the rotating disc are mounted for exposure to the cooler incoming gas flow to avoid overheating. The seals around the rotating disc, however, are necessarily exposed to relatively hot gas and special precautions are made to avoid overheating. Since this system uses a flat disc, little mass is available for transferring heat from outlet to inlet.
See also U.S. Pat. Nos. 2,121,733; 3,167,400; 3,172,251; 3,211,534; 3,634,026; 3,870,474; 3,895,918; 3,997,294; 4,302,426; 4,474,118; 4,650,414; 4,678,634; 4,793,974.
Accordingly, there is a need for an enhanced regenerative gas treatment system that has enhanced efficiency, utilizes its gas permeable blocks more effectively; and keeps the heated areas confined so that moving parts are not unnecessarily exposed to high temperatures.